1. Field of the Invention
The present invention relates to a voice coil having a bobbin and a coil, and a speaker including the voice coil.
2. Description of the Related Art
In a dynamic speaker, a bobbin is vibrated by a change of a current flowing through a coil wound around a bobbin, and vibrations thus generated are transmitted to a diaphragm. Accordingly, as a material that forms the bobbin of the voice coil, it is preferable to select a material that easily transmits vibrations to the diaphragm, are lightweight and strong.
Various materials such as kraft, aluminum, aramid fiber and polyimide have been used for a conventional voice coil bobbin (for example, Japanese Unexamined Patent Application Laid-Open (Koukai) No. 2002-300697). However, the conventional materials have merits and demerits and there have not been obtained yet a single material for a voice coil bobbin which has a high propagation velocity, is lightweight and strong, and is capable of suppressing its vibration loss smaller.
In addition, there have been proposed that a voice coil bobbin on which a metallic layer is deposited on an entire surface of a resin film base (for example, Japanese Unexamined Patent Application Laid-open (Koukai) No. H11-341596). However, the voice coil bobbin on which the metallic layer is deposited is unsuitable for voice coil bobbins of a full-range and mid/treble speakers because the metallic layer deposited on the entire surface of the resin film base increases a weight of the bobbin.
For use in bobbins of the full-range and mid/treble speakers, it has been desired to reduce the weight of the bobbin by thinning a thickness thereof. However, when the thickness of the bobbin is too thin, a portion which is not wound around a coil becomes structurally weakened, and accordingly, a treble resonance and a vibration loss may occur.